The present invention relates to a resin composition having an oxygen scavenging function. The present invention also relates to a resin composition having good gas barrier properties, moisture-resistance, aroma retentivity, and flavor barrier properties, in addition to the oxygen scavenging function, and a multilayered container made of such a resin composition.
Gas barrier resins such as ethylene-vinyl alcohol copolymer (hereinafter also abbreviated as EVOH) can be melt-molded, and have excellent gas barrier properties against oxygen or carbon dioxide gas. For this reason, a multilayered structure including a layer made of EVOH, for example, and a layer made of a thermoplastic resin having excellent moisture-resistance, mechanical properties or the like (e.g., thermoplastic polyester; hereinafter thermoplastic polyester may be abbreviated as PES) is utilized for various molded products (e.g., films, sheets, bottles, containers, etc.) that require gas barrier properties. For example, such multilayered structures are used in various fields as a multilayered container, in particular, in the form of bags, bottles, cups, pouches, etc. For example, they are widely used in such fields as foods, cosmetics, medicines, toiletries and the like.
Such a multilayered container has good barrier properties against oxygen, carbon dioxide gas, and the like. However, its permeability of gases such as oxygen is not exactly zero, unlike metals used for cans, etc. and glass used for bottles, etc. but still permits transmission of gas in an amount that cannot be neglected. In particular, for containers of foods, the degradation of food contents due to oxidation when the food is preserved for a long time is of great concern. Therefore, improvement of the oxygen barrier properties is strongly desired.
Furthermore, when filling the contents into a container, oxygen may be mixed in the container together with the contents. When the contents are susceptible to oxidization, even a trace amount of oxygen may degrade the quality of the contents. In order to prevent this, providing a material of the container with an oxygen scavenging function has been proposed. In this case, oxygen that might enter the container from the outside can be scavenged, so that the gas barrier properties of a packaging material also can be improved.
For example, as the method of providing the oxygen scavenging function to the gas barrier resin that constitutes a packaging material, the following methods are known: (1) An oxidation catalyst such as a transition metal is added to the EVOH to make the EVOH susceptible to oxidation, thereby providing the EVOH with the oxygen scavenging function (Japanese Laid-Open Patent Publication (Tokkai) No.4-211444); (2) A metal catalyst is added to polyvinyl chloride to make polyvinyl chloride susceptible to oxidation, thereby providing the polyvinyl chloride with the oxygen scavenging function (Japanese Laid-Open Patent Publication (Tokkai) No.4-45144); (3) A resin composition mainly comprising polyolefin and an oxidation catalyst, that is, polyolefin in a state susceptible to oxidation, is dispersed in the EVOH, thereby providing the EVOH with the oxygen scavenging function (Japanese Laid-Open Patent Publication (Tokkai) No.5-156095); and (4) EVOH, polyolefin, and an oxidation catalyst are blended to make the EVOH and polyolefin susceptible to oxidation, thereby providing the oxygen scavenging function (Japanese Laid-Open Patent Publication (Tokkai) No.5-170980). However, methods (1) and (2) fail to provide sufficiently improved oxygen barrier properties. Methods (3) and (4) have the disadvantage that the transparency of the gas barrier resin is impaired significantly.
Furthermore, in multilayered containers, especially when no adhesive resin layer is provided between the layers and the container filled with a drink or food is subjected to an impact caused by, for example, being dropped, delamination between the thermoplastic resin layer (e.g., PES layer) and the EVOH layer is likely to occur, which causes a large problem in the appearance.
It is an object of the present invention to provide a composition having an oxygen scavenging function. It is another object of the present invention to provide a resin composition having good gas barrier properties, transparency, moisture-resistance, aroma retentivity, and flavor barrier properties, in addition to the oxygen scavenging function. It is still another object of the present invention to provide a multilayered container including a layer made of the resin composition having a good impact delamination resistance and good appearance, in particular, satisfactory transparency.
A first resin composition of the present invention comprises a gas barrier resin (A), a thermoplastic resin (B) other than the gas barrier resin (A) and a compatibilizer (C), wherein the gas barrier resin (A) has an oxygen transmission rate of 500 mlxc2x720 xcexcm/m2xc2x7daysxc2x7atm (20xc2x0 C., 65% RH) or less, the thermoplastic resin (B) has a carbonxe2x80x94carbon double bond, and an oxygen absorption rate of the resin composition is 0.001 ml/m2xc2x7day or more.
In a preferred embodiment, the first resin composition further comprises a transition metal salt (D).
A second resin composition of the present invention comprises a gas barrier resin (A), a thermoplastic resin (B) other than the gas barrier resin (A), a compatibilizer (C) and a transition metal salt (D), wherein the gas barrier resin (A) has an oxygen transmission rate of 500 mlxc2x720 xcexcm/m2xc2x7dayxc2x7atm (20xc2x0 C., 65% RH) or less, and the thermoplastic resin (B) has a carbonxe2x80x94carbon double bond.
In a preferred embodiment, the amount of the transition metal salt (D) contained in the first or second resin composition (when the first resin composition comprises the transition metal salt (D)) is 1 to 5000 ppm in terms of the metal element, based on a total weight of the gas barrier resin (A), the thermoplastic resin (B), and the compatibilizer (C).
In a preferred embodiment, the transition metal salt (D) comprises at least one transition metal selected from the group consisting of iron, nickel, copper, manganese, and cobalt.
In a preferred embodiment, the thermoplastic resin (B) comprises a carbonxe2x80x94carbon double bond in a ratio of 0.0001 eq/g or more.
In a preferred embodiment, the thermoplastic resin (B) comprises a unit represented by formula (I) 
wherein R1 is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, R2 is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an aryl group, an alkylaryl group, an arylalkyl group or an alkoxy group, R3 and R4 are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an aryl group that can be substituted, xe2x80x94COOR5, xe2x80x94OCOR6, a cyano group or a halogen atom, and R5 and R6 are each independently an alkyl group having 1 to 10 carbon atoms, an aryl group, an alkylaryl group, an arylalkyl group or an alkoxy group.
In a preferred embodiment, a number average molecular weight of the thermoplastic resin (B) is 1000 to 500000.
In a preferred embodiment, the gas barrier resin (A) is an ethylene-vinyl alcohol copolymer having an ethylene content of 5 to 60 mol % and a degree of saponification of 90% or more.
In a preferred embodiment, a difference in refractive index between the gas barrier resin (A) and the thermoplastic resin (B) is 0.01 or less.
In a preferred embodiment, in the above-mentioned resin compositions, particles of the thermoplastic resin (B) are dispersed in a matrix of the gas barrier resin (A).
In a preferred embodiment, each of the first and second resin compositions comprises 40 to 99.8 wt % of the gas barrier resin (A), 0.1 to 30 wt % of the thermoplastic resin (B), and 0.1 to 30 wt % of the compatibilizer (C).
A third resin composition of the present invention comprises a thermoplastic resin (B) and a compatibilizer (C), wherein the thermoplastic resin (B) comprises a unit represented by formula (I) 
(wherein R1 is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, R2 is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an aryl group, an alkylaryl group, an arylalkyl group or an alkoxy group, R3 and R4 are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an aryl group that can be substituted, xe2x80x94COOR5, xe2x80x94OCOR6, a cyano group or a halogen atom, and R5 and R6 are each independently an alkyl group having 1 to 10 carbon atoms, an aryl group, an alkylaryl group, an arylalkyl group or an alkoxy group); the thermoplastic resin (B) has a carbonxe2x80x94carbon double bond in a ratio of 0.0001 eq/g or more; a number average molecular weight of the thermoplastic resin (B) is 1000 to 500000; and an oxygen absorption rate of the resin composition is 0.1 ml/m2xc2x7day or more.
In a preferred embodiment, the third resin composition further comprises a transition metal salt (D).
A fourth resin composition of the present invention comprises a thermoplastic resin (B), a compatibilizer (C), and a transition metal salt (D), wherein the thermoplastic resin (B) comprises a unit represented by formula 
(wherein R1 is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, R2 is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an aryl group, an alkylaryl group, an arylalkyl group or an alkoxy group, R3 and R4 are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an aryl group that can be substituted, xe2x80x94COOR5, xe2x80x94OCOR6, a cyano group or a halogen atom, and R5 and R6 are each independently an alkyl group having 1 to 10 carbon atoms, an aryl group, an alkylaryl group, an arylalkyl group or an alkoxy group); the thermoplastic resin (B) has a carbonxe2x80x94carbon double bond in a ratio of 0.0001 eq/g or more, and a number average molecular weight of the thermoplastic resin (B) is 1000 to 500000.
In a preferred embodiment, the amount of transition metal salt (D) contained in the third or fourth resin composition (when the third resin composition comprises the transition metal salt (D)) is 1 to 50000 ppm in terms of the metal element, based on a total weight of the thermoplastic resin (B) and the compatibilizer (C).
In a preferred embodiment, the transition metal salt (D) contained in the third or fourth resin composition (when the third resin composition comprises the transition metal salt (D)) comprises at least one transition metal selected from the group consisting of iron, nickel, copper, manganese, and cobalt.
In a preferred embodiment, the compatibilizer (C) is a thermoplastic resin having at least one functional group selected from the group consisting of a carboxyl group, a boronic acid group and a boron-containing group that can be converted to a boronic acid group in a presence of water.
In a preferred embodiment, the thermoplastic resin (B) comprises an aromatic vinyl compound unit and a diene compound unit.
In a preferred embodiment, the diene compound unit is at least one of an isoprene unit and a butadiene unit.
In a preferred embodiment, the aromatic vinyl compound unit is a styrene unit.
In a preferred embodiment, the thermoplastic resin (B) is a block copolymer.
A multilayered structure of the present invention comprises at least one layer made of any one of the first to fourth resin compositions.
A multilayered container of the present invention comprises at least one layer made of any one of the first to fourth resin compositions and at least one thermoplastic polyester layer.
A cap of the present invention comprises a gasket made of any one of the first to fourth resin compositions, wherein the gasket is mounted on a cap body.